1. Field of the Invention
The present invention relates generally to the field of ocular surgery, and more specifically to managing fluid levels within a reservoir using a capacitive sensor device for measuring the reservoir fluid level during ophthalmic procedures such as the removal of a cataract.
2. Description of the Related Art
Phacoemulsification surgery has been successfully employed in the treatment of certain ocular problems, such as cataract surgery, including removal of a cataract-damaged lens and implanting an artificial intraocular lens. Phacoemulsification surgery typically involves removal of the cataract-damaged lens and may utilize a small incision at the edge of the patient's cornea. Through the small incision, the surgeon then creates an opening in the capsule, i.e. membrane that encapsulates the lens.
Next, the surgeon may insert an ultrasonic probe, incorporated within the phacoemulsification handpiece, through the opening in the cornea and capsule accessing the damaged lens. The handpiece's ultrasonic actuated tip emulsifies the damaged lens sufficient to be evacuated by the handpiece. After the damaged natural lens is completely removed, the handpiece tip is withdrawn from the patient. The surgeon may now implant an intraocular lens into the space made available in the capsule.
While performing phacoemulsification surgical techniques, such as lens removal, the surgeon may control a pump to pull fluids from the eye and through the handpiece tip. The pump is configured with a tank or reservoir positioned to hold the fluid until the tank fills to a certain point or level. During emulsification of the damaged lens, the tip of the phaco handpiece may collect fluids from the patient's eye and transfer the fluids for holding or temporarily storing in the reservoir. As the tip further collects fluid and material, the reservoir may fill with fluid to a point where the ratio of the volume of air with respect to the volume of fluid in the reservoir is outside of a desirable operating range. Typically, the desired operating range may dictate a minimum volume required for venting and reflux, a maximum volume to prevent the pump from exposure to fluids or from working into an uncompressible volume, and an intermediate or target volume representing a desired air-to-fluid ratio. During an ocular procedure, the air-to-fluid ratio may reach a point where the reservoir requires “rebalancing,” which involves adding fluid to, or removing fluid from, the reservoir for the purpose of maintaining the desired operational ratio.
During the surgery it may become necessary for the surgeon to be able to remove fluid from a reservoir, or tank, into a waste or collection bag for the purpose of rebalancing the reservoir. One method for rebalancing the reservoir, when the fluid level exceeds the desirable operating range, involves the outflow of fluid and materials from the reservoir into a collection bag using a pump. When the fluid reaches a certain level the pump is turned on and removes or drains the reservoir. Alternatively, if the fluid level in the reservoir falls below a low level threshold, rebalancing may involve the inflow of fluid from the collection bag or from an infusion bottle into the reservoir. In either arrangement, when the reservoir air-to-fluid ratio is returned within desirable operating values, indicating the reservoir is ‘balanced’ the pump is stopped which in turn stops the flow of fluid and materials.
Maintaining a proper air-to-fluid ratio or balance within the reservoir may allow the surgeon to perform various aspiration, vacuum venting, and reflux surgical procedures without interruption. When the reservoir level reaches an upper lever threshold, thus requiring outflow or removal of fluid, the instrument host typically turns on a pump to move the fluid from the reservoir to the collection bag.
In order to remove fluid, current designs typically determine the proper time to activate a peristaltic reservoir pump by sensing the fluid level in the reservoir. Today's designs typically involve either a float mechanism, an optical or sound emitter-sensor system, using for example infrared light and ultrasonic frequencies.
Many of today's designs integrate the reservoir with other components, such as pumps, selector valves, and surgical tubing, into a surgical cassette system. The surgical cassette system is situated between the handpiece and collection bag and may provide an interface for a vacuum pump and peristaltic pump operations.
For example, Advanced Medical Optics, Inc. (AMO) of Santa Ana, Calif. offers a phacoemulsification medical system that has dual pump capability and employs a specific replaceable surgical cassette that enables dual pump operation and can be changed after a surgical procedure. A dual pump surgical cassette exhibiting an efficient reservoir fluid level sensing arrangement that can manage the reservoir's air-to-fluid ratio by controlling pump operation is highly desirable. Certain designs may include operating the opening and closing of a valve to allow gravity to empty contents from the reservoir into the collection bag in lieu of operating the pump.
Controlling mechanized fluid outflow and inflow for a surgical cassette reservoir by sensing devices that enable precise determination of the fluid level within the reservoir for operating a pump is often desirable in an operating room situation. While certain sensor devices have previously been offered, reliability in air-fluid reservoir balancing in these cassettes can at times be imperfect, particularly in precise operating environments.
Some previous designs include a float mechanism, which can fail by sticking to the side of the reservoir, or the float may “sink” into the reservoir. Optical and sound mechanisms tend to be costly to deploy, and in certain cases are unreliable when the sensing path is subjected to condensation, droplets, debris, or foam. It would be beneficial to offer a surgical cassette that employs minimal components or components that efficiently control and maintain the fluid level within the cassette reservoir as required in the ocular surgical environment.